As a need for semiconductor integrated circuits having a higher integration density is currently increasing, the lithography process for manufacturing semiconductor devices uses a light source of shorter wavelength. At present, the photolithography using ArF excimer laser (193 nm) is the mainstream. A future transition of photolithography to extreme ultraviolet (EUV) is regarded promising to gain a higher integration density. Like the photolithography, the nanoimprint technology is also in the limelight for the fabrication of semiconductor devices having a half pitch of 32 nm or less.
The nanoimprint technology is expected to find diversified applications of fabricating optical waveguides, biochips, and optical storage media. In the nanoimprint technology, a mold (also referred to as stamper or template) is engraved with a topological or fine pattern formed by EB exposure or etching technology. The mold is pressed to a resin material or resist layer coated on a substrate to transfer the fine pattern to the resin layer. In the fabrication of semiconductor devices, for example, the mold is pressed to a resist layer coated on a semiconductor wafer, typically silicon wafer to transfer the fine pattern to the resist layer.
In the step of pressing the mold to a resist layer on a recipient substrate to transfer the fine pattern to the resist layer, the mold must be pressed such that even fine recesses of the pattern over its entire extent may be filled with the resin material. If the resin material is incompletely spread, with air bubbles left, the fine pattern on the mold is not completely transferred.
For this reason, the transfer step is generally carried out in a least viscous gas atmosphere, for example, a helium-containing atmosphere so that no bubbles are left behind.
If the step of pressing the mold to a resin material is slowed down, residual bubbles may be minimized or eliminated. However, the slow step is one of barriers against the application of the nanoimprint technology to semiconductor fabrication because the semiconductor fabrication process requires to increase the throughput, that is, the number of processed units in a given time.
It is regarded effective for eliminating residual bubbles that helium gas in bubbles is absorbed and transmitted by the mold. While the nanoimprint mold is generally made of synthetic quartz glass having excellent light transmittance, thermal stability, mechanical properties and working properties, the glass has a low helium gas permeability and thus makes only a little contribution to throughput improvement.
Then WO 2011/096368 discloses a mold made of TiO2—SiO2 glass having a high helium gas permeability. The TiO2—SiO2 glass has the advantage that its light transmittance and thermal stability are equivalent or superior to synthetic quartz glass.